In recent years, digital broadcasting has adopted orthogonal frequency division multiplex (hereinafter, OFDM) systems. Such systems including the OFDM systems are suitable for mobile reception of digital broadcasting and have been put to practical use in, for example, car navigation systems and portable phones. Digital broadcasting has also adopted a diversity reception technique using a plurality of antennas in order to improve mobile reception performance.
A channel selection requires a channel selection table showing the correspondence between the channel number and the broadcaster. The channel selection table showing the correspondence between the channel number having a program on the air and the broadcaster should be formed (hereinafter, channel search) by searching all channels every time the mobile receiving terminal moves from one region to another. This is because the channel assignment for broadcasters differs from region to region.
The channel search in a digital broadcasting receiving apparatus generally requires two steps. The first step is to set the frequency to the receiver and to detect whether or not synchronization has been established. The second step is to perform error correction and decoding in the subsequent stages when synchronization has been established and to acquire the broadcaster name. In the second step, time interleaving and decoding are particularly time-consuming, making the channel search time much longer than in analog broadcasting.
To reduce the channel search time, it has been suggested to utilize a diversity receiving apparatus having a plurality of receivers. For example, one receiver can be used to view a program (hereinafter, single reception) and the other receiver can be used to perform a channel search. Alternatively, a plurality of receivers can be used to receive a plurality of channels and to select the channels sequentially.
One of the prior arts related to such methods is Patent Document 1 shown below.
A channel search in single reception, however, is likely to cause detection failure because the sensitivity of single reception is lower than that of diversity reception, namely, by about 3 dB. For example, when single reception has an image reproduction sensitivity of −99 dB, diversity reception has an image reproduction sensitivity of −102 dB. As a result, in a reception environment with an electric field intensity of, for example, −100 dB, a signal can be received by diversity reception, but not be detected by a channel search in single reception.
Furthermore, small terminals generally cannot adopt the technique of receiving a signal by one receiver and performing a channel search by the other receiver. This is because in general small terminals have two receivers to perform diversity reception, but have only one error corrector and one decoder such as an MPEG decoder for decoding compressed signals in order to reduce size and power consumption. In this structure, the error corrector and the decoder are occupied while a signal is being received by one receiver, making it impossible for the other receiver to execute the above-described second step in the channel search.
Patent Document 1: Japanese Patent Unexamined Publication No. 2006-13689